Microstructure of the pyrocarbon in aligned carbon nanotube/carbon composites

Aligned carbon nanotube reinforced carbon matrix(ACNT/C)composites were fabricated by densifying an ACNT preform with chemical vapor infiltration(CVI)and their microstructure was investigated by XRD,SEM,HRTEM,polarized light microscopy and Raman spectroscopy.Results show that the pyrocarbon in ACNT/C composites was of mainly rough lamella type,while that in traditional carbon/carbon composites obtained using the same process was of typically smooth lamella type with a larger interlayer spacing and a smaller layer stack height.Pyrocarbon around CNTs shows a clear annular graphitic-layered microstructure with good interfacial bonding between CNTs and pyrocarbon.This might be ascribed to the intermolecular interaction between CNTs and aromatic molecules,i.e.,CNTs have abundant radial delocalized conjugated π-π electrons,which can attract polynuclear aromatic molecules with a similar structure through van der Waals forces.These polynuclear aromatic molecules are therefore oriented around the CNT outer surface under a soft epitaxy mechanism.In contrast,carbon fibers composed of turbostratic carbon have no such effect during CVI.